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Question

JSTL fmt library throws 500 error, requires sessions enabled?

Answer 1

+1 A:

That's very unfortunate. It look like you can't go around this. Your best bet is then to create custom EL functions which does the same. Here's an example how you could replace fmt:formatDate.

First create an EL functions class (just a simple static class):

package com.example;

import java.text.SimpleDateFormat;
import java.util.Date;

public final class Functions {

    private Functions() {
        //
    }

    public static String formatDate(Date date, String pattern) {
        return new SimpleDateFormat(pattern).format(date);
    }

}

Then create a /WEB-INF/functions.tld (note: JSP 2.1 targeted, not sure what your GAE supports, it's maybe Servlet 2.4, if so then you need to redeclare it as JSP 2.0 taglib):

<?xml version="1.0" encoding="UTF-8" ?>

<taglib 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
    version="2.1">

    <display-name>Custom Functions</display-name>    
    <tlib-version>1.0</tlib-version>
    <uri>http://example.com/functions&lt;/uri&gt;

    <function>
        <name>formatDate</name>
        <function-class>com.example.Functions</function-class>
        <function-signature>java.lang.String formatDate(java.util.Date, java.lang.String)</function-signature>
    </function>
</taglib>

Then you can use it as follows in your JSP:

<%@taglib uri="http://example.com/functions" prefix="f" %>
<jsp:useBean id="date" class="java.util.Date" />
...
<p>Current year: ${f:formatDate(date, 'yyyy')}</p>

BalusC 2010-08-12 23:32:44

Hey there BalusC, thanks for your feedback and suggestion. I think this would be good, longer-term solution, but I would like to try and use the JSTL fmt library instead of having to re-implement the functionality myself. By the way, I find your weblog very informative and have learned a lot from reading your informative articles, tutorials, and your other response here on stackoverflow. Thanks for sharing!

Curt 2010-08-16 23:33:40

You're welcome :) Good luck with this issue.

BalusC 2010-08-17 02:46:34

Answer 2

A:

While waiting to see what the full stacktrace reveals, here's another option. This filter will look for JSTL config params in web.xml and set them as request attributes in the hope that this will short-circuit any need for GAE to access the session:

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.jsp.jstl.core.Config;

public class JSTLConfigFilter implements Filter {

    private static final String[] JSTL_CONFIG_PARAMS = { Config.FMT_FALLBACK_LOCALE,
                                                         Config.FMT_LOCALE,
                                                         Config.FMT_LOCALIZATION_CONTEXT,
                                                         Config.FMT_TIME_ZONE,
                                                         Config.SQL_DATA_SOURCE,
                                                         Config.SQL_MAX_ROWS };
    private final Map<String, String> jstlConfig = new ConcurrentHashMap<String, String>();

    public void init(FilterConfig config) throws ServletException {
        ServletContext ctx = config.getServletContext();
        for (String param : JSTL_CONFIG_PARAMS) {
            String value = ctx.getInitParameter(param);
            if (value != null) {
                this.jstlConfig.put(param, value);
            }
        }
    }

    public void destroy() {
        this.jstlConfig.clear();
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        for (Map.Entry<String, String> entry : this.jstlConfig.entrySet()) {
            Config.set(request, entry.getKey(), entry.getValue());
        }
        chain.doFilter(request, response);
    }
}

Variations are, of course, possible, but hopefully you get the idea...

kschneid 2010-08-16 18:54:01

Thanks for your feedback. I implemented the Filter as you describe above, however disabling sessions still causes and error. I appended the stack trace to my question above.

Curt 2010-08-17 02:46:17

the stacktrace indicates that the issue is with `<fmt:setLocale>`. how are you using it in your page? i believe one of the side-effects of `<fmt:setLocale>` is to try and store the response's char encoding in a session attribute. however, it should only do this if `PageContext.getSession()` is not null...

kschneid 2010-08-17 03:44:26

Answer 3

A:

Code wich cause the issue is in fmt lib SetLocaleSupport class is

    static void setResponseLocale(PageContext pc, Locale locale) {
    .../...
// get response character encoding and store it in session attribute
if (pc.getSession() != null) {
        try {
        pc.setAttribute(RequestEncodingSupport.REQUEST_CHAR_SET,
            response.getCharacterEncoding(),
            PageContext.SESSION_SCOPE);
        } catch (IllegalStateException ex) {} // invalidated session ignored
}
}

it blindlessly put the charset in session. You can't do much...

JeanLaurent 2010-08-18 15:27:37

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JSTL fmt library throws 500 error, requires sessions enabled?

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